1. Field of the Invention
The present invention relates to an electrophotographic, photosensitive member and an image forming apparatus having the photosensitive member and, more particularly, to an electrophotographic, photosensitive member capable of achieving lower cost and an image forming apparatus (electrophotographic apparatus) making use of the so-called electrophotographic system having the photosensitive member.
2. Related Background Art
It is required that a photoconductive material for forming a photoconductive layer in an image forming member for electrophotography in the field of formation of image have the following characteristics; for example, having high sensitivity, a high S/N ratio [photocurrent (Ip)/dark current (Id)], absorption spectral characteristics matched with spectral characteristics of an electromagnetic wave radiated thereto (which is light in a general sense, such as ultraviolet light, visible light, infrared light, X-ray, .gamma.-ray, or the like), quick optical response, and a desired dark resistance, being nonpolluting to human bodies during use, and so on. Particularly, in the case of the image forming members for electrophotography incorporated in electrophotographic apparatus used as business machines in offices, the above-stated nonpolluting property during use is a significant point.
On the basis of this viewpoint, for example, German Patent Application Laid-Open Nos. 2746967 and 2855718 describe the application of amorphous silicon in which dangling bonds are compensated with a univalent element such as hydrogen (H), halogen (X), or the like (hereinafter referred to as a-Si(H,X)), to the image forming members for electrophotography, and such materials are applied to the image forming members for electrophotography because of their excellent photoconductive property, wear resistance, and heat resistance, and relative easiness of increase of area to a larger area.
In producing a photosensitive drum for electrophotography having the photoconductive material containing a-Si(H,X), in order to obtain good photoconductive characteristics, it is common practice to deposit an a-Si(H,X) film in the thickness of 1 to 100 .mu.m on a drum-like metal substrate under such a condition that the drum-like metal substrate is continuously heated at relatively higher temperature, 200.degree. C. to 350.degree. C., than in the case of Se-based materials, in an a-Si(H,X) film deposition system. This maintenance of heating of the substrate at the high temperature is necessary for production of the a-Si-based photosensitive drum with excellent electrophotographic characteristics and it is the present status that this maintenance of heating at the high temperature ranges from several hours to somewhat more than 10 hours, based on consideration of deposition rates of the a-Si(H,X) film.
The photoconductive member for electrophotography, in its preferred embodiment, is constructed in such structure that a drum-like, or cylindrical, metal substrate of Al or an Al alloy or the like (hereinafter referred to as an Al-based substrate) is used as a metal support for the photoconductive member for electrophotography and that a photoconductive layer containing an amorphous material having the matrix of silicon and preferably containing at least either one of hydrogen and halogen as a constituent element is formed on the drum-like Al-based metal substrate. The photoconductive layer may have a blocking layer in contact with the drum-like metal substrate and further have a surface blocking layer in the surface of the photoconductive layer.
FIGS. 1A and 1B are views for explaining an example of the layer structure of the a-Si photosensitive member.
FIG. 1A is a schematic, perspective view, in which reference numeral 2100 indicates the thickness of the photosensitive member including a support 2101 and a photoreceptive layer 2105.
FIG. 1B is a schematic, sectional view, in which on the electroconductive substrate 2101 of aluminum or the like there are successively stacked layers, i.e., a charge injection inhibiting layer 2102 for inhibiting injection of charge from the conductive support 2101, and a photoconductive layer 2103 for creating electrons and holes with irradiation of light and converting image information to potential information. Each of these layers is comprised of a material having the matrix of amorphous silicon and, if necessary, containing a neutralizer of the dangling bonds, such as hydrogen and/or halogen, or the like, a valency controller of an element belonging to Group III, Group V, or the like, a modifying substance such as oxygen, carbon, nitrogen, or the like, and so on as occasion may demand. On the upper surface of the photoconductive layer 2103 in the figure, there is provided a surface protecting layer 2104 for protecting the photoconductive layer from friction or the like against a developer, a transfer sheet, a cleaning device, etc. and for preventing charge from being injected from the surface to the photoconductive layer. The surface protecting layer 2104 is comprised of a material of a-SiC:H with excellent light transmittancy to the photoconductive layer, excellent mechanical strength, excellent effect of preventing injection of charge from the top, and so on.
Materials preferably used as a base material for the drum-like (hollow cylinder shape) metal substrate are, for example, metals such as NiCr, stainless steel, Al, Cr, Mo, Au, Nb, Ta, V, Ti, Pt, Pd, and so on, or alloys thereof. Particularly, Al and Al-based alloys are preferably applicable.
The reasons why aluminum or the aluminum-based alloys are preferably used as a base material for the drum-like substrate are that it is relatively easy to obtain the substrate with high accuracies of roundness, surface smoothness, etc., it is easy to control the temperature of the surface part of the a-Si(H,X) deposition during production, and they are economical.
The halogen atoms (X) which the photoconductive layer of the photoconductive member may contain are, specifically, fluorine, chlorine, bromine, or iodine, among which chlorine is particularly preferred and fluorine is more particularly preferred. The photoconductive layer can contain another component or other components than the silicon atoms, hydrogen atoms, and halogen atoms, as a valency controller, as a modifying substance, or the like, as described above, which are one or an appropriate combination selected from the atoms belonging to Group III of the periodic table such as boron, gallium, and so on (hereinafter referred to as III atoms), the atoms belonging to Group V of the periodic table such as nitrogen, phosphorus, arsenic, etc. (hereinafter referred to as V atoms), oxygen atoms, carbon atoms, germanium atoms, etc. as a component for controlling the Fermi level, the bandgap, and so on.
The blocking layer is provided for the purpose of enhancing the adhesion between the photoconductive layer and the drum-like metal substrate or for the purpose of controlling charge receptibility or the like and the blocking layer is constructed in a single layer or in multiple layers of a-Si(H,X) or polycrystal-Si containing III atoms, V atoms, oxygen atoms, carbon atoms, germanium atoms, etc. according to the purpose.
The layer above the photoconductive layer may be provided as a surface charge injection inhibiting layer or as a protecting layer, which is a layer comprised of an amorphous material having the matrix of silicon atoms, containing carbon atoms, nitrogen atoms, oxygen atoms, etc., preferably, in a large amount and, if necessary, containing hydrogen atoms or halogen atoms, or a layer comprised of a high-resistance organic substance.
The photoconductive layer comprised of a-Si(H,X) is formed by conventionally known vacuum deposition methods utilizing various discharge phenomena, for example, such as a glow discharge method, a sputtering method, an ion plating method, and so on.
Next described is an example of a method for producing the photoconductive member (photosensitive member) for electrophotography by the glow discharge decomposition method.
FIG. 2 shows an example of a system for producing the photosensitive member for electrophotography by the glow discharge decomposition method. A deposition chamber 1 is constructed of a base plate 2, a wall 3, and a top plate 4, and a cathode electrode 5 of a cylindrical shape is provided inside the deposition chamber 1. A drum-like metal substrate 6 on which an a-Si(H,X) deposited film is to be deposited is set in the central part of the cathode electrode 5 (at the center of concentric circles) and also serves as an anode electrode.
For forming the a-Si(H,X) deposited film on the drum-like metal substrate by this production system, first, a source gas inflow valve 7 and a leak valve 8 are closed and an exhaust valve 9 is opened to evacuate the inside of the deposition chamber 1. When the reading of a vacuum gage 10 reaches about 5.times.10.sup.-6 Torr, the source gas inflow valve 7 is opened to allow a source mixture gas, for example, of SiH.sub.4 gas, Si.sub.2 H.sub.6 gas, SiF.sub.4 gas, etc., adjusted at a predetermined mixture ratio in a mass flow controller 11 to flow into the deposition chamber 1. At this time the ratio of the value opening of the exhaust valve 9 is adjusted by checking the reading of the vacuum gage 10 so that the pressure inside the deposition chamber 1 becomes a desired value. After it is confirmed that the surface temperature of the drum-like metal substrate 6 is set at a prescribed temperature by a heater 12, a high-frequency power supply 13 is set to a desired power to bring about glow discharge in the deposition chamber 1.
During execution of formation of the layer the drum-like metal substrate 6 is rotated at a constant rate by a motor 14 in order to uniformly deposit the layer. The a-Si(H,X) deposited film can be formed on the drum-like metal substrate 6 in this way.
However, because of the difference between coefficients of thermal expansion of the drum-like metal substrate and the a-Si(H,X) film and large internal stress in the a-Si(H,X) film formed, it was not rare to encounter peeling of the a-Si(H,X) film off the drum-like metal substrate, not only during the deposition of the a-Si(H,X) film in which the drum-like metal substrate was maintained as heated at the high temperature, as described previously, but also during the period of cooling down to the temperature of the outside atmosphere after the deposition. Further, there were more than a few cases in which the a-Si(H,X) film was peeled off because of heating of the drum depending upon the temperature of the operating environment during the use as a photosensitive drum for electrophotography. The film peeling off in the case of the a-Si(H,X) film occurred more readily as the thickness of the a-Si(H,X) film became larger. With thermal deformation of the drum-like metal substrate (which is, particularly, easy to occur during the formation of the photoconductive layer) even in such a degree as not to cause the film to peel off in the case of the conventional Se-based electrophotographic, photosensitive drums, there were more than a few cases in which the film peeling off occurred in the case of the a-Si(H,X)-based photosensitive drums, for the reason of the aforementioned difference between coefficients of thermal expansion and the magnitude of the internal stress in the a-Si(H,X) film. The internal stress in the a-Si(H,X) film can be relaxed to some extent by production conditions of the a-Si(H,X) film (kinds of source gases, a ratio of flow rates of the gases, discharge power, the heating temperature of the substrate, the internal structure of the production system, etc.), but production conditions are not yet sufficient yet when consideration is given to productivity and mass productivity. This film peeling off will cause image defects and be fatal in application to the photosensitive drum for electrophotography.
The high-temperature heating of the drum-like metal substrate over a long period during the production of the a-Si(H,X) film can be the cause of the above film peeling off and also make the thermal deformation of the drum-like metal substrate happen more readily. This thermal deformation causes nonuniformity of discharge during the production of the a-Si(H,X) deposited film, whereby evenness of thickness of the a-Si(H,X) deposited film is lost, which would be the cause of the image defects.
In view of the various points discussed above, an example of the photoconductive member for electrophotography intended to reduce the image defects is one in which the drum-like metal substrate is comprised of aluminum or an aluminum-based alloy and the thickness is not less than 2.5 mm, for example, as described in Japanese Patent Publication No. 6-14189.
Taking the recent cutthroat price competition and, particularly, development to middle- and low-speed models into consideration making operating cost low is not enough, and the point is how much the initial cost can be decreased. Therefore, an urgent necessity was to decrease the cost of the photoconductive member drastically.
The percentage of the raw material cost was large in the cost of the photoconductive member and decrease in the thickness of the drum-like metal substrate was thus expected to realize not only simple reduction of the raw material cost, but also additional cost reduction, including power savings and decrease in tack time resulting from decrease of the heating time during the production of the a-Si(H,X) film, a cutback of the power for maintaining the high temperature, decrease in the tack time resulting from reduction of the cooling time, and so on, for the reason of the low heat capacity resulting from the small thickness. Therefore, there were urgent desires for cost reduction of the drum-like metal substrate and improvement in temperature characteristics.